Apparatus for milling foundry sand



Feb. 4, 1969 F. M. SHAW 3,425,670

APPARATUS FOR MILLING FOUNDRY SAND Filed Aug. 16, 1967 FIGZ.

United States Patent Office 3,425,670 Patented Feb. 4, 1969 37,859/ 66 US. Cl. 259--72 Int. Cl. B01f 9/08; B28c /18 5 Claims ABSTRACT OF THE DISCLOSURE A mill for foundry sand comprises an elongated trough which is resiliently supported and is oscillated laterally and vertically by an out-of-balance shaft, and the trough contains a single large roller extending the length of the trough and at least a quarter of its diameter.

Foundry sand normally consists of grains of refractory such as silica with a proportion of clay which, when moistened, forms the bond to cause the grains to adhere and makes it possible to form moulds into which molten metal can be cast. Foundry sand also contains other minor materials, such as coal dust, to impart particular founding characteristics to the mould, and small quantities of material to impart strength or plasticity.

In order that the correct moulding properties may be developed it is necessary to mill the sand prior to use. The milling operation involves not only mixing but also rubbing the clay, which distributes it, and the water content in it, and develops its bonding characteristics. The most common form of sand mill involves a circular container in which plough and a heavy roller revolve, the action being one of mixing and kneading. In such mills the rollers are weighted or spring-loaded but do not in fact touch the bottom of the mill. It is important not to crush the sand grains during the milling operation since degradation of the sand resulting from crushing of the grains will change the properties of the sand and make it finally unusable. This type of mill is known as a batch mill, into which a specific quantity of sand is added, appropriate additions of water and other materials are made and mixing takes place for a definite period of time, for example three minutes.

Many attempts have been made to develop continuous mills, since the tendency in mechanised foundries is to circulate sand continuously and it would be very desirable for the mill to handle the sand without intermittent operation. The continuous milling of sand presents difiiculties because of the problem of ensuring that the sand remains in the mill long enough for it to be uniformly mixed and kneaded, and so issue from the mill as a uniform product. Continuous mills have been proposed which consist of long, circular shells in which spiral ploughs and/or agitators, and long rollers revolve, the sand being fed in at one end and issuin at the other. Other types of continuous mills have involved the provision of special feeding arrangements to circular mills, used either singly or in combination, in which heavy rollers revolve so that sand continuously enters and leaves the mill through some special gate arrangements.

For the purpose of cleaning or deburring metal objects such as sand castings or articles to be plated or painted, it is well known that one type of equipment used to achieve this object is a vibratory container. This affords a means of rapidly vibrating articles to be cleaned, frequently together with an abrasive ceramic material and water. The rubbing action ensuing cleans the objects put into the container and removes roughness from them if suitably operated. Vibratory containers of this kind are energised by electro-magnetic means or by a mechanical out-of-balance drive. Vibratory milling is also a well known means of crushing granular materials to fine powders. This is done in a vibrated container with a number of balls in it when the granular material is fed in, and constitutes an efiicient means of grinding such materials. Such an apparatus could be used for milling sand, but its action would not be acceptable for foundries because the sand grains become broken and degradation results.

According to this invention we propose a vibratory foundry sand mill comprising a substantially horizontal container having a troughed lower portion, a loose roller axially disposed in and extending lengthwise of the troughed portion, and means for vibrating the container in a manner such that longitudinal lines on the container describe circular or elliptical paths whereby the roller is caused to revolve within the troughed portion.

Preferably at least one of the contacting surfaces of the roller and the container has a flexible coating, for example a rubber coating.

We prefer that the container should have a flexible coating although it will be apparent from the following description that the coating might be on the roller or indeed there might be a coating on the roller and the container.

In tests it has been found that with such a mill the roller revolves slowly and the sand passes continuously under the roller. Such a mill can be operated either as a batch mill or as a continuous mill. In the latter case continuity is achieved by slowly feeding sand to one end of the mill and allowing it to flow over a discharge gate at the other end of the mill.

We find that the efiiciency of the mill varies with the weight of the roller and with the diameter of the roller relatively to the size of the container. We find that the rollers will generally occupy up to half of the available volume of the mill body, and preferably will occupy about a quarter of the available volume. The sand would then occupy the greater part of the remaining space. The roller would normally be a hollow metal cylinder, for instance cast iron, and because it is loose in the mill it will be easy to replace when it becomes worn.

An example of such a mill is illustrated in the accompanying drawings of which:

FIGURE 1 is an end view of a schematic arrangement of a mill according to the invention and FIGURE 2 is a side view, partly cutaway, of the arrangement of FIGURE 1.

The mill comprises a troughed container in the form of a circular body 10 with open top 11 and discharge grid 12 at one end. It is mounted on springs '13, 13a and driven by a mechanically out-of-balance shaft 14 running at 1,650 rev/min. in bearings (not shown) in the lower part of the 'body 10. The shaft 14 produces an out-ofbalance force, of approximately 1.74 tonf. The rotating shaft 14 is arranged to vibrate the body 10 at an average amplitude of ,4, in. in the horizontal direction and in. in the vertical direction, i.e. the motion'is elliptical.

Loosely placed in the container is a roller 15 which is about the same length as the interior of the mill body and is about half the diameter of the interior of the mill body thus to occupy about a quarter of the available volume of the body. The roller 15 has a diameter of 10.25 in., a length of 23.5 in. and weighs 128 lbs.

The mill has a rubber lining which prevents or reduces attrition of the sand grains. In operation the roller rotates but does not touch the sides of the mill and kneads a layer of sand which continuously circulates around the mill and under the roller. Another favourable 3 action of the mill is that it causes aeration of the sand at the discharge point 12.

The capacity of the mill is five cubic feet and 256 lb. of sand, containing 3 percent water and 5 percent of bentonite clay, can be milled in the mill in approximately two minutes.

An advantage of the process is that the mill contains no moving parts other than the loose roller described. This means that problems of replacement and repair become very much less than with other types of mill. The roller itself is easily replaced, and replaceable wearing plates (not shown) may be fitted to the inside of the ends of the mill and replaced at the same time as the rollers.

What is claimed is:

1. A vibrating mill for foundry sand comprising a resiliently supported substantially horizontal container having a troughed lower portion, a single loose roller disposed axially in said container and extending lengthwise of said troughed portion, said roller having a volume not less than one quarter of the volume of said container, and drive means operatively connected to said container, said drive means being operative to vibrate said coHainer in a plurality of directions transverse to the length thereof, whereby to cause said roller and the contents being 4 treated in said container to revolve within said troughed portion.

2. A rnill as set forth in claim 1, wherein at least one of the contacting surfaces of said container and said roller bears a flexible coating.

3. A mill as set forth in claim 2 wherein said flexible coating is on the inner surface of said container.

4. A mill as set forth in claim 1 wherein said roller has a volume not more than half the volume of said container.

5. A mill as set forth in claim 1 wherein said roller and said container are both of substantially cylindrical form.

References Cited UNITED STATES PATENTS 1,908,104 5/1933 Bell 25972 2,143,610 1/1939 Muller 2592 2,208,077 7/ 1940 Linke 2592 X 2,222,777 11/ 1940 Linke 2592 X 3,271,012 9/1966 Bael 25929 ROBERT W. JENKINS, Primary Examiner.

US. Cl. X.R. 

